Method For Producing Carbonyl Difluoride

ABSTRACT

The present invention relates to a method for producing carbonyl difluoride comprising a step of reacting trifluoromethane with oxygen or an oxygen-containing gas while heating.

TECHNICAL FIELD

The present invention relates to a method for producing carbonyldifluoride.

BACKGROUND OF THE INVENTION

Carbonyl difluoride is a useful material having various uses such as amaterial for fluoroorganic compounds, a cleaning gas for use infabricating semiconductors, etc.

Examples of known methods for producing carbonyl difluoride using carbonmonoxide as a starting material include methods wherein carbon monoxideis subjected to electrolytic fluorination (Patent Document 1), andwherein carbon monoxide is directly fluorinated using fluorine gas(Non-Patent Document 1). Examples of known methods using phosgene as astarting material include methods wherein phosgene is fluorinated usinghydrogen fluoride in the presence of solvent, phosgene is fluorinatedusing hydrogen fluoride in the presence of solvent and triethylamine(Patent Document 2), phosgene is fluorinated using sodium fluoride in asolvent (Patent Document 3), and phosgene is fluorinated in the vaporphase using hydrogen fluoride together with an activated carbon catalyst(Patent Document 4). It is also known that carbonyl difluoride can beproduced by reacting tetrafluoroethylene (TFE) with oxygen (PatentDocument 5).

However, electrolytic fluorination and direct fluorination, which aremethods for producing carbonyl difluoride using carbon monoxide as astarting material, require an expensive electrolytic vessel and/or alarge facility for controlling the large amount of reaction heat, andare thus not preferable for industrial use. In electrolytic fluorinationof carbon monoxide, CF₄ and CF₃OF are produced as byproducts, and indirect fluorination of carbon monoxide, CF₃OF and like peroxides aregenerated as byproducts. Furthermore, the selectivity for carbonyldifluoride is low. Among the methods using phosgene, particularly inmethods wherein phosgene is fluorinated using hydrogen fluoride in thepresence of solvent, and methods wherein phosgene is fluorinated usinghydrogen fluoride and an activated carbon catalyst, it is difficult toseparate the generated carbonyl difluoride from hydrogen chloridebecause they have a small difference in boiling points (about 1° C.). Inmethods wherein phosgene is fluorinated using hydrogen fluoride in thepresence of solvent and triethylamine or methods wherein phosgene isfluorinated using sodium fluoride in the presence of solvent, carbonyldifluoride can be obtained without generation of hydrogen chloride, butlarge amounts of triethylamine hydrochloride and sodium chloride aregenerated and therefore waste treatment and/or reuse/recycling thereofis necessary.

The reaction wherein TFE is oxidized using oxygen generates an extremelylarge amount of reaction heat, and therefore there is a risk of anexplosion.

Furthermore, it is difficult to obtain large amounts of carbon monoxide,phosgene, and TFE, as are used in the above-mentioned productionmethods, because they are toxic and/or unstable, and careful handling isrequired.

Examples of readily obtainable materials include chlorodifluoromethane(HCFC22), and trifluoromethane (HFC23). Known production methods usingthese starting materials include: reacting HCFC22 or likemonohalo-difluoromethane with oxygen (Patent Document 6), and reactingHCFC22 with ozone (Non-Patent Document 2). It is also known, althoughnot as a production method, that carbonyl difluoride can be generated byreacting HFC23 with O(¹D), which is an electronically excited oxygenatom (Non-Patent Document 3).

In Patent Document 6, generation of carbonyl difluoride was confirmedbut not quantified. Patent Document 6 nowhere discloses what byproductswere generated. In Non-Patent Document 2, in addition to carbonyldifluoride, HCl, Cl₂, and unidentified byproducts are generated. Here,the obtained HCl has a boiling point near that of carbonyl difluoride,and therefore it is difficult to separate the HCl from the carbonyldifluoride. HFC23 is a trihalogenated methane similar to HCFC22;however, it is known that HFC23 does not cause generation of HCl as abyproduct, because it does not contain chlorine, and the reactivity ofHFC23 is very different from that of HCFC22. For example, theirlifetimes in air according to the IPCC (evaluated based on the reactionspeed with an OH radical, which is an oxidizing agent stronger than O₂)(Non-Patent Document 4) are as follows. The lifetime of HCFC22 is 11.9years, that of HFC23 is 260 years, and that of CHBrF₂, which is anexample of another trihalogenated methane, is 7 years. It is known that,compared to other trihalogenated methanes, HFC23 has an extremely lowreactivity. Therefore, it is impossible to predict that carbonyldifluoride can be formed from HFC23 using the same methods as disclosedin Patent Document 6 and Non-Patent Document 2. The method disclosed inNon-Patent Document 3 uses a reaction with highly excited oxygen, and isfundamentally different from that of the present invention. Furthermore,it is industrially difficult to put the method disclosed in Non-PatentDocument 3 to practical use, and, as with Patent Document 6,quantification was not conducted. According to Non-Patent Document 3,CO₂ is excited by laser, O(³P) is generated in addition to O(¹D), andO(³P) does not relate to the reaction with HFC23. It is known that O(¹D)generates carbonyl difluoride by reacting with HFC23, and is thenchanged to O(³p) by being deactivated due to collision with thegenerated carbonyl difluoride (Non-Patent Document 5). This is not veryefficient reaction. It is also known that O(¹D) reacts with carbonyldifluoride and some portion thereof decomposes into CO₂ and F₂(Non-Patent Document 5); however, because F₂ is more oxidative than O₂,when carbonyl difluoride is reacted with O₂, carbonyl difluoride doesnot decompose into CO₂ and F₂.

As described above, many methods for producing carbonyl difluoride,including methods using fluorinated methane compounds as startingmaterials, have been published; however, a reaction achieving a highyield through a simple method has not yet been founded.

[Patent Document 1] Japanese Examined Patent Publication No. S45-26611

[Patent Document 2] Japanese Unexamined Patent Publication No.S54-158396

[Patent Document 3] U.S. Pat. No. 3,088,975

[Patent Document 4] U.S. Pat. No. 2,836,622

[Patent Document 5] U.S. Pat. No. 3,639,429

[Patent Document 6] EP0310255

-   [Non-Patent Document 1] J. Am. Chem. Soc., Vol. 91, (1969) pp.    4432-4436-   [Non-Patent Document 2] Chemical Abstracts Vol. 93, No. 13,    (1980), p. 621 Abstracts No. 132037x-   [Non-Patent Document 3] Chemistry Letters (1992), pp. 1309-1312-   [Non-Patent Document 4] Climate Change 2001: The Scientific Basis-   [Non-Patent Document 5] Chemical Physics Letters Vol. 69, (1983),    pp. 129-132-   [Non-Patent Document 6] Zeitschrift fur Anorganische und Allgemeine    Chemie Vol. 242, (1939), pp. 272-276

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present invention provides an economical method for providingcarbonyl difluoride, which is useful for various purposes such as amaterial for fluoroorganic compounds, a cleaning gas for fabricatingsemiconductors, etc.

Means for Solving the Problem

The present inventors conducted extensive research to achieve the aboveobject and found that carbonyl difluoride can be obtained in high yieldby reacting trifluoromethane with oxygen (oxygen gas, or air,oxygen-enriched air or like oxygen-containing gas) while heating.Furthermore, by using a corrosion resistive reaction vessel, the amountof byproduct CO₂ can be greatly reduced.

The present invention provides the following methods:

1. A method for producing carbonyl difluoride comprising the step ofreacting trifluoromethane with oxygen gas or an oxygen-containing gaswhile heating.

2. A method for producing carbonyl difluoride according to Item 1,wherein the reaction temperature is in the range of from 100° C. to1500° C.

3. A method for producing carbonyl difluoride according to Item 1 or 2,wherein the oxygen-containing gas is air or an oxygen-enriched gashaving a higher oxygen content than air.

4. A method for producing carbonyl difluoride according to any one ofItems 1 to 3, wherein the amount of byproduct CO₂ is reduced by reactingtrifluoromethane with the oxygen gas or oxygen-containing gas in acorrosion resistive reaction vessel.

5. A method for producing carbonyl difluoride according to any one ofItems 1 to 4, wherein the reaction is conducted in the presence of acatalyst.

6. A method for producing carbonyl difluoride by reactingtrifluoromethane with oxygen gas or an oxygen-containing gas in areaction vessel while heating comprising the steps of:

(i) increasing the pressure of raw product gas generated in the reactionvessel using a compressor if necessary, cooling the raw product gas in acooler, separating the resulting gas into an oxygen-rich gas and aliquid component, and returning the oxygen-rich gas to the reactionvessel; and

(ii) distilling the liquid component separated from the oxygen-rich gasin Step (i) by using a distillation column, collecting highly purifiedcarbonyl difluoride, and returning concentrated trifluoromethane to thereaction vessel.

7. A method for producing carbonyl difluoride by reactingtrifluoromethane with oxygen gas or an oxygen-containing gas in areaction vessel while heating comprising the steps of:

(i) increasing the pressure of raw product gas generated in the reactionvessel using a compressor if necessary, cooling the raw product gas in acooler, and removing HF by liquefaction;

(ii) further increasing the pressure of the gas not liquefied in Step(i) using a compressor if necessary, cooling the gas in a cooler,separating an oxygen-rich gas from a liquid component, and returning theoxygen-rich gas to the reaction vessel; and

(iii) distilling the liquid component separated in Step (ii) by using adistillation column, collecting highly purified carbonyl difluoride, andreturning concentrated trifluoromethane to the reaction vessel.

Effect of the Invention

The present invention makes it possible to efficiently produce carbonyldifluoride. HFC23 used as a raw material in the present invention is agreenhouse gas. However, because it can be obtained as a byproduct ofHCFC22, which is used as a cooling medium or a raw material for TFE, andsome HFC23 is used as an etching gas but most is incinerated, fullyutilizing such HFC23 is economically and environmentally verymeaningful.

BEST MODE FOR CARRYING OUT THE INVENTION

The reaction of the present invention is expressed by the chemicalreaction as below.2CHF₃+O₂→2COF₂+2HF

There is no limitation to the method for conducting the presentreaction, and a standard vapor phase reaction method can be employed. Inother words, the method is for continuously or batchwisely producing araw product by continuously or batchwisely supplying trifluoromethane(which may be referred to as “HFC23”) and oxygen gas/oxygen-containinggas to a heated reaction chamber. In many cases, the raw productcontains CO₂ (byproduct) in addition to carbonyl difluoride and HF, but,depending on the reaction conditions, sometimes the raw product containsa large amount of unreacted HFC23 and/or oxygen, and sometimes verylittle CO₂, and/or small amounts of other byproducts.

Compounds contained in the raw product other than carbonyl difluoridecan be separated by distillation, etc., if necessary. Compounds otherthan the separated carbonyl difluoride, such as unreacted HFC23 andoxygen (carbonyl difluoride may be additionally included) can bereused/recycled in the reaction system. Therefore, there is no problemeven if a large amount of carbonyl difluoride is included with thesecompounds when separated from carbonyl difluoride. Furthermore,materials having a boiling point greatly different from that of carbonyldifluoride, such as HF and oxygen, can be separated without conductingseparation using a cooling distillation, etc., by subjecting the rawproduct to compression and/or cooling. For example, HF and compoundshaving a boiling point higher than oxygen can be separated by selectiveliquefaction.

When air or oxygen-enriched air is used as oxygen, air oroxygen-enriched air can be separated, collected, reused, etc., in thesame manner as oxygen.

With respect to the conditions for reacting HFC23 with oxygen (oxygengas or oxygen-containing gas), the reaction proceeds faster and moreefficiently when the reaction temperature is higher, but if thetemperature is unduly high, CO₂ (byproduct) increases and is thus notpreferable. Specifically, the reaction temperature is generally about100° C. to about 1500° C., preferably about 300° C. to about 1000° C.,and more preferably about 350° C. to about 700° C. If the reactiontemperature is too low, the reaction speed becomes extremely slow andthe reaction time is prolonged, and is thus not effective. Furthermore,if the reaction temperature is too high, not only the production ofbyproducts increases, but the lifetime of the reaction vessel alsodecreases due to corrosion, etc., and thus is also not preferable.

The reaction time varies depending on the reaction temperature, but isgenerally about 0.1 seconds to about 10 hours, preferably about 0.5seconds to about 1 hour, and more preferably about 1 second to about 30minutes. The longer the reaction time becomes, the more the reactionprogresses, but an unduly long reaction time may result in heating morethan necessary and is therefore inefficient. If the reaction time is tooshort, the reaction does not satisfactorily progress and separation ofthe generated carbonyl difluoride becomes difficult, and is thus alsoinefficient.

The proportion of HFC23 to oxygen (O₂) may be suitably selected, but theproportion of oxygen relative to 1 mole of HFC23 is generally about 0.01moles to about 200 moles, preferably about 0.1 moles to about 100 moles,and more preferably about 0.5 moles to about 50 moles. Theoretically,0.5 moles of oxygen reacts with 1 mole of HFC23, but even if the amountof oxygen is smaller than this, it does not cause any problem in thereaction. However, if the amount of oxygen is too small, the amount ofcarbonyl difluoride generated is also small, and this adversely affectsefficiency. Using excessive oxygen is efficient because the reaction canbe promoted and the amount of carbonyl difluoride generated isincreased. Unreacted oxygen can be recycled by sending it back to thereaction system, but if the amount thereof is unduly large, the amountof oxygen to be recycled becomes too large. This necessitates a largefacility, and is thus uneconomical.

Air and air whose oxygen concentration is increased by anoxygen-enriched membrane, etc., can be used as an oxygen-containing gas.There is no limitation to the oxygen concentration of such anoxygen-containing gas, as long as the reaction can proceed, but isgenerally in the range of from about 10% v/v to less than 100% v/v, andpreferably from about 20% v/v to less than 100% v/v. There is no problemeven if the oxygen concentration is lower than air.

It is preferable that water and CO₂ be removed from air before reactionby compression, cooling, and/or using an adsorbent. The proportion ofoxygen to HFC23 when such air is used is the same as described above.

The reaction pressure can be suitably selected as either lower thanstandard atmospheric pressure, or not less than standard atmosphericpressure, but the higher the pressure becomes, the more efficient, andmore preferable for the separation subsequently conducted. Specifically,the pressure is generally in the range of from −0.09 MPaG to 20 MPaG ingauge pressure, and preferably from standard atmospheric pressure to 20MPaG for making the process simple, and more preferably from standardatmospheric pressure to 10 MPaG considering the pressure resistance ofthe vessel or like equipment.

The material(s) of the reaction vessel in the portion(s) contacting thereaction gas is important. As long as they can resist oxygen and HF athigh temperatures, various kinds of metals and inorganic substances canbe used, including iron, copper, and alloys containing large amounts ofiron and/or copper; however, because CO₂ and CO are formed when thesemetals react with the generated carbonyl difluoride under oxygenatmospheres at high temperatures, the yield of carbonyl difluoride isdecreased. Therefore, corrosion resistive materials, such as SUS316 andlike stainless steels, HASTELLOY C and like Ni—Cr—Mo alloys, INCONEL600and like Ni—Cr alloys, HASTELLOY B and like Ni—Mo alloys, MONEL400 andlike Ni—Cu alloys and other nickel alloys, pure nickel, etc., arepreferably used. Even stainless steel sometimes causes decomposition ofcarbonyl difluoride, and therefore Ni—Cr alloys, Ni—Mo alloys, Ni—Cr—Moalloys, Ni—Cu alloys and like nickel alloys, and nickel and like highlycorrosion resistive materials are more preferably used. In addition tothe above-mentioned alloys, it is also possible to use iron andstainless steels as materials for the reaction vessel as long as theycan resist an oxygen-containing atmosphere at high temperatures bycoating the reaction vessel with sodium fluoride, potassium fluoride,calcium fluoride and like stable metal fluorides.

One of the main features of the present invention is thattrifluoromethane is reacted with oxygen under a heated atmosphere;however, it is known that some portion of carbonyl difluoride decomposesinto CO₂ and CF₄ when a nickel or platinum catalyst is used under aheated atmosphere (Non-Patent Document 6). Regardless that anickel-based reaction vessel is used or nickel beads are placed in thereaction vessel, CF₄ is not formed due to decomposition of the generatedcarbonyl difluoride in the present invention, probably because thereaction is conducted in the presence of oxygen.

Likewise in a standard vapor phase reaction, a catalyst(s) may be usedin the present invention. It is also possible to place pellets or beadsin the reaction vessel as a heat-transmission medium. It is preferablethat the materials for pellets or beads be selected from those that donot decompose carbonyl difluoride, such as sodium fluoride pellets,nickel beads, etc.

Examples of usable catalysts include ruthenium, rhodium, palladium,osmium, iridium, platinum, and silver, as well as fluorides of aluminum,manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum,silver, cadmium, tin, hafnium, rhenium, thallium, lead, bismuth, etc.These fluorides do not have to be fluorides when prepared, and may bechlorides, bromides, oxides, etc. For example, CoCl₂, MnBr₂, MgCl₂,CuCl₂, etc., are highly soluble in methanol, and therefore they can bereadily supported on a carrier. The prepared catalyst can be fluorinatedby contacting with COF₂, HF, etc., before or during the reaction.Catalysts in the platinum group are formed by supporting a metal halideon a carrier, and reducing it using hydrogen, etc., and thethus-obtained resultant catalysts are used in the reaction. Examples ofusable carriers supporting such catalysts include NaF, KF and likealkali metal fluorides; and MgF₂, CaF₂, BaF₂ and like alkaline-earthmetal fluorides.

The reaction in the present invention can be conducted by a productionprocess, for example, as illustrated in FIGS. 1 and 2.

The production process illustrated in FIG. 1 can be conducted in such amanner as described below.

(1) The raw product gas released from the reaction vessel has itspressure raised using a compressor 1, if necessary. If the raw productgas has a satisfactorily high pressure, compression is unnecessary.

(2) The gas, having its pressure raised if necessary, is cooled in acooler 1, and gases having boiling points higher than oxygen areliquefied and stored in a receiver 1. The liquid stored in the receiver1 is supplied to a distillation step from a vapor phase portion orliquid phase portion in a form of gas or liquid. It is also possible tosupply only a carbonyl difluoride-rich phase to the subsequent step, ifHF and carbonyl difluoride are separated from each other by cooling thereceiver 1.

(3) The gas not liquefied in the cooler 1 is a gas containing a largeamount of oxygen and therefore returned to the reaction vessel afterbeing controlled its pressure using a pressure regulating valve, etc.

(4) The liquid stored in the receiver 1 is supplied to the distillationstep without modification, and then separated into highly purifiedcarbonyl difluoride, a mixture of HFC23 and carbonyl difluoride, andconcentrated HF. Of those, the mixture of HFC23 and carbonyl difluorideis returned to the reaction vessel. Depending on the proportions of theconstituent components of the material supplied to the distillation stepand the distillation conditions, highly purified carbonyl difluoride isusually obtained from the top portion of the column and a mixture ofHFC23 and carbonyl difluoride is obtained from the middle portion of thecolumn.

The process illustrated in FIG. 2 can be conducted in the followingmanner.

(1) The raw product gas released from the reaction vessel has itspressure raised using a compressor 1, if necessary, and is cooled in acooler 1. HF, having a high boiling point, is liquefied and stored in areceiver 1. If the raw product gas has a satisfactorily high pressure,compression is unnecessary.

(2) The gas not liquefied in the cooler 1 has its pressure furtherraised by a compressor 2 and then cooled in a cooler 2. Almost all thegases having a boiling point higher than oxygen are liquefied and storedin a receiver 2.

(3) The gas not liquefied in the cooler 2 is a gas containing a largeamount of oxygen and can therefore be returned to the reaction vesselafter having its pressure controlled using a pressure regulating valve,etc.

(4) The liquid stored in the receiver 2 is supplied to the distillationstep without modification, and then separated into highly purifiedcarbonyl difluoride, a mixture of HFC23 and carbonyl difluoride, andconcentrated HF. Of those, the mixture of HFC23 and carbonyl difluorideis returned to the reaction vessel. Depending on the proportions of theconstituent components of the material supplied to the distillation stepand distillation conditions, highly purified carbonyl difluoride isusually obtained from the top portion of the column and the mixture ofHFC23 and carbonyl difluoride is obtained from the middle portion of thecolumn.

In the embodiments shown in FIGS. 1 and 2, air or air whose oxygenconcentration is increased by an oxygen-enriched membrane, etc., may beused instead of oxygen. In this case, it is preferable that impuritiessuch water and carbon dioxide be reduced by absorption, compression,cooling, etc.

The raw product gas released from the reaction vessel may be used forheating raw materials via a heat exchanger.

If the pressure in the reaction vessel is satisfactorily high, thecompressor is unnecessary.

EXAMPLES

Hereunder, the present invention is explained in detail with referenceto Examples; however, the present invention is not limited to theseExamples.

Example 1

Using a ring-shaped heater, a SUS316 reaction chamber (heating portionof about 30 cm) having an external diameter of ¾ of an inch was heatedto a predetermined temperature while supplying nitrogen. HFC23 andoxygen were supplied at a specified flow rate at the same temperature.The reaction chamber had a gauge pressure of about 0.01 MPaG. The gasreleased from the reaction chamber was diluted with about 1 L/minnitrogen, and then analyzed by FTIR. Table 1 shows the evaluatedconversion of trifluoromethane and selectivities for the product gas.

Examples 2 to 6

A reaction was conducted in the same manner as in Example 1 except thatabout 20 ml of NaF pellets (3 mm Φ×3 mm H) were placed in a heatingportion of the reaction chamber. Table 1 shows the results.

Examples 7 to 9

Using a ring-shaped heater, a HASTELLOY C reaction chamber (heatingportion of about 50 cm) having an inside diameter of about 2 cm washeated to a predetermined temperature while supplying nitrogen. At thistemperature, HFC23 and oxygen were supplied at a specified flow rate.The reaction chamber had a gauge pressure of about 0.01 MPaG. The gasreleased from the reaction chamber was diluted with about 1 L/minnitrogen, and then analyzed by FTIR. Table 1 shows the evaluatedconversion of trifluoromethane and selectivities for the product gas.

Examples 10 to 16

A reaction was conducted in the same manner as in Example 7 except thatabout 40 ml of nickel beads (2 mm Φ) were placed in a heating portion ofthe reaction chamber. Table 1 shows the results.

Examples 17 to 19

Using a ring-shaped heater, a nickel reaction chamber (heating portionof about 50 cm) having an external diameter of ⅜ of an inch was heatedto a predetermined temperature while supplying nitrogen. At thistemperature, HFC23 and oxygen were supplied at a specified flow rate.The reaction chamber had a gauge pressure of about 0.01 MPaG. The gasreleased from the reaction chamber was diluted with about 1 L/minnitrogen, and then analyzed by FTIR. Table 1 shows the evaluatedconversion of trifluoromethane and selectivities for the product gas.

The residence times of the gases in the heating portions were calculatedbased on the volume of the heating portion, flow rate of raw material,and reaction temperature. The results are as follows: 18 seconds inExample 17, 12 seconds in Example 18, and 9 seconds in Example 19. TABLE1 Selectivity Temper- Trifluoro- O₂ Conversion for carbonyl aturemethane (ml/ of trifluoro- difluoride (° C.) (ml/min) min) methane (%)(%) Example 1 518 14 14 86 80 Example 2 520 14 14 88 88 Example 3 460 1414 83 89 Example 4 491 22.6 5.7 51 87 Example 5 480 5.5 22.7 76 75Example 6 540 28 28 67 60 Example 7 550 5.2 10.6 91 99 Example 8 600 5.220.5 97 99 Example 9 600 5.2 10.6 97 98 Example 10 600 5.2 10.6 98 97Example 11 700 5.2 10.6 99.9 87 Example 12 520 18.3 35.9 99 99.8 Example13 520 26.9 27.1 98 99.6 Example 14 420 17.1 33.3 91 99.9 Example 15 38017.1 33.3 81 99.9 Example 16 350 5.2 5.2 64 99.9 Example 17 450 10 20 9099.8 Example 18 450 15 30 52 99.8 Example 19 450 20 40 5 97.6

From the results of the above Examples, it became clear that theHASTELLOY C reaction chamber is superior to the others.

The results also indicate that Examples 12 and 13 have excellentreaction temperatures (520° C.). Example 11 has a low selectivitybecause of its high reaction temperature. Examples 14 to 16 have highselectivities, but long reactions are necessary because of the lowtemperatures, and presumably this decreases the conversion oftrifluoromethane.

From the above results, it can be concluded that a preferable reactiontemperature is in the range of from 400° C. to 600° C. If thetemperature is lower than this range, the conversion of trifluoromethanebecomes low, and if the temperature is higher than this range,byproducts are generated and selectivity is reduced.

Example 20

A reaction chamber was heated to 520° C. in the same manner as inExample 10, and then HFC23 (5.2 ml/min), oxygen (10.1 ml/min), andnitrogen (39.8 ml/min) were supplied. The gas released from the reactionchamber was analyzed by FTIR without modification. The conversion oftrifluoromethane and selectivity were evaluated and the results indicatethat the conversion of trifluoromethane was 80%, and the selectivity forcarbonyl difluoride was 99.5%.

Reference Example 1

Using a ring-shaped heater, a SUS316 reaction chamber (heating portionof about 20 cm) having an external diameter of ¾ of an inch whereinabout 100 ml of NaF pellets were placed in the heating portion washeated to 520° C. while supplying nitrogen, and carbonyl difluoride (9ml/min) and a mixture of oxygen/nitrogen (20/80 vol, 171 ml/min) werethen supplied while maintaining the temperature. The gas released fromthe reaction chamber was analyzed by FTIR without modification, andformation of a small amount of CO₂ was confirmed. The inside of thereaction chamber was observed after completion of the reaction, whereinthere was no change in the NaF pellets but corrosion was observed in thereaction chamber.

In contrast, decomposition of carbonyl difluoride into CO₂ can bereduced by using a reaction chamber of Ni—Cr alloy, Ni—Mo alloy,Ni—Cr—Mo alloy, Ni—Cu alloy or like nickel alloy, or nickel or likecorrosion resistive material instead of an SUS316 reaction chamber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows one example of a COF₂ production process of the presentinvention.

FIG. 2 shows another example of a COF₂ production process of the presentinvention.

1: A method for producing carbonyl difluoride comprising the step ofreacting trifluoromethane with oxygen gas or an oxygen-containing gaswhile heating. 2: A method for producing carbonyl difluoride accordingto claim 1, wherein the reaction temperature is in the range of from100° C. to 1500° C. 3: A method for producing carbonyl difluorideaccording to claim 2, wherein the oxygen-containing gas in air or anoxygen-enriched gas having a higher oxygen content than air. 4: A methodfor producing carbonyl difluoride according to claim 3, wherein theamount of byproduct CO₂ is reduced by reacting trifluoromethane with theoxygen gas or oxygen-containing gas in a corrosion resistive reactionvessel. 5: A method for producing carbonyl difluoride according to claim4, wherein the reaction is conducted in the presence of a catalyst. 6: Amethod for producing carbonyl difluoride by reacting trifluoromethanewith oxygen gas or a oxygen-containing gas in a reaction vessel whileheating comprising the steps of: (i) increasing the pressure of rawproduct gas generated in the reaction vessel using compressor ifnecessary, cooling the raw product gas in a cooler, separating theresulting gas into an oxygen-rich gas and a liquid component, andreturning the oxygen-rich gas to the reaction vessel; and (ii)distilling the liquid component separated from the oxygen-rich gas inStep (i) by using a distillation column, collecting highly purifiedcarbonyl difluoride, and returning concentrated trifluoromethane to thereaction vessel.
 7. A method for producing carbonyl difluoride byreacting trifluoromethane with oxygen gas or a oxygen-containing gas ina reaction vessel while heating comprising the steps of: (i) increasingthe pressure of raw product gas generated in the reaction vessel usingcompressor if necessary, cooling the raw product gas in a cooler, andremoving HF by liquefaction; (ii) further increasing the pressure of thegas not liquefied in Step (i) using a compressor if necessary, coolingthe gas in a cooler, separating an oxygen-rich gas from a liquidcomponent, and returning the oxygen-rich gas to the reaction vessel; and(iii) distilling the liquid component separated from the oxygen-rich gasin Step (ii) by using a distillation column, collecting highly purifiedcarbonyl difluoride, and returning concentrated trifluoromethane to thereaction vessel. 8: A method for producing carbonyl difluoride accordingto claim 1, wherein the oxygen-containing gas in air or anoxygen-enriched gas having a higher oxygen content than air. 9: A methodfor producing carbonyl difluoride according to claim 8, wherein theamount of byproduct CO₂ is reduced by reacting trifluoromethane with theoxygen gas or oxygen-containing gas in a corrosion resistive reactionvessel. 10: A method for producing carbonyl difluoride according toclaim 9, wherein the reaction is conducted in the presence of acatalyst. 11: A method for producing carbonyl difluoride according toclaim 1, wherein the amount of byproduct CO₂ is reduced by reactingtrifluoromethane with the oxygen gas or oxygen-containing gas in acorrosion resistive reaction vessel. 12: A method for producing carbonyldifluoride according to claim 11, wherein the reaction is conducted inthe presence of a catalyst. 13: A method for producing carbonyldifluoride according to claim 2, wherein the amount of byproduct CO₂ isreduced by reacting trifluoromethane with the oxygen gas oroxygen-containing gas in a corrosion resistive reaction vessel. 14: Amethod for producing carbonyl difluoride according to claim 13, whereinthe reaction is conducted in the presence of a catalyst. 15: A methodfor producing carbonyl difluoride according to claim 1, wherein thereaction is conducted in the presence of a catalyst. 16: A method forproducing carbonyl difluoride according to claim 2, wherein the reactionis conducted in the presence of a catalyst. 17: A method for producingcarbonyl difluoride according to claim 3, wherein the reaction isconducted in the presence of a catalyst.